Exploring the regolith with electrical resistivity tomography in large-scale surveys: electrode spacing-related issues and possibility

Gourdol, Laurent; Clément, Rémi; Juilleret, Jérôme; Pfister, Laurent; Hissler, Christophe

doi:https://doi.org/10.5194/hess-25-1785-2021

Articles | Volume 25, issue 4

https://doi.org/10.5194/hess-25-1785-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-25-1785-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 25, issue 4

Research article

|

07 Apr 2021

Research article |

| 07 Apr 2021

Exploring the regolith with electrical resistivity tomography in large-scale surveys: electrode spacing-related issues and possibility

Laurent Gourdol, Rémi Clément, Jérôme Juilleret, Laurent Pfister, and Christophe Hissler

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Final revised paper (published on 07 Apr 2021)
Supplement to the final revised paper
Preprint (discussion started on 31 Jul 2020)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'misprints and comments', Anonymous Referee #1, 06 Sep 2020
- AC1: 'Comments_on_hess-2018-374-RC1&RC2 from Anonymous Referee #1', Gourdol Laurent, 12 Nov 2020
RC2: 'General comment', Anonymous Referee #1, 06 Sep 2020
- AC2: 'Comments_on_hess-2018-374-RC1&RC2 from Anonymous Referee #1', Gourdol Laurent, 12 Nov 2020
RC3: 'Review comments', Anonymous Referee #2, 01 Oct 2020
- AC3: 'Comments_on_hess-2018-374-RC3 from Anonymous Referee #2', Gourdol Laurent, 12 Nov 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (17 Nov 2020) by Alberto Guadagnini

AR by Gourdol Laurent on behalf of the Authors (18 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (03 Feb 2021) by Alberto Guadagnini

RR by Anonymous Referee #2 (08 Feb 2021)

Suggestions for revision or reasons for rejection

I would like to thank the authors for this revised version of the manuscript, and more specifically for the detailed answers to the initial comments. The authors have addressed a series of concerns on the originality of the study, and I must admit that their justification as to why this work is worth publishing in HESS is totally reasonable. I have no major objections anymore for this study to be considered for publication in HESS (after clarifying some remaining points of concerns). However, is worth mentioning that even though I’m satisfied with the author’s rebuttal, the revised version of the manuscript remains in essence rather similar to the first version, and was not substantially modified, as one would have expected after a “major revision”.

The proposed novel procedure for ERT measurements, which is the main focus of the manuscript, and described in Sect. 2.3 remains too poorly explained in this revised version of the manuscript, and I’m afraid is still subject to misunderstanding. The new figure 4 illustrating the novel approach is clearly a really good addition to help capturing the main concept, but, apologies for this, I still struggle to understand the method. The authors state in their answer to the editor that in the original version of the manuscript, the reader might miss a key step of the proposed procedure. The new version of the manuscript does not seem to bring much more explanation on this key step, as no improvement of the manuscript has been included in Sect. 2.3 of the methodology to support the new Figure 4. The missing key point concerns what data are used in the linear regressions. It is indeed not clear what data are plotted against each other on the scatter plots (Fig. 6 and Fig. 10). I know realise that this might come from a missing information in the first step detailed in Sect. 2.3, which states that “from the set of apparent resistivity data measured with an ES of 2 m, we extract the first acquisition level of apparent resistivity data (for the smallest possible external electrodes separation, i.e. 6 m). For this acquisition level, we extract – from the set of apparent resistivity data relying on an ES of 0.5 m – four subsets of apparent resistivity data for smaller external electrodes separations of 1.5, 2.5, 3.5 and 4.5 m, respectively.” There is no information as to what these subsets are made of. Is it the apparent resistivity of the measurement array which has the pseudo-x position closest to that of the array with the larger ES? Is it an average of the apparent resistivities for all the arrays of a specific smaller ES comprised within the larger ES? As things stand, the reader can only guess what this subset is made of, and I would suggest the authors to explain in much more detail how it is extracted. It wouldn’t arm anyway to have a slightly more detailed Sect 2.3 of the manuscript. This is the claimed main novelty of the study, so I would really strengthen the explanation of the method. In the current version of the manuscript, there is a rather shortly explained method, with lengthy examples, but if the method is not clear in the first place, the examples are not really helpful. Clarifying how the subsets are extracted in the legends of Fig. 6 and Fig 10 would also be welcomed.

A practical aspect of the proposed method could also be included in the discussions. Indeed, have the authors investigated the appropriate number of ERT profiles with smaller ES needed to improve significantly the accuracy of the ERT measurements with larger ES? It could be interesting to assess if using a smaller number of ERT profiles than the 12 field datasets gives similar results. Since the area seems to have a rather constant solum thickness, could only 1 ERT profile with smaller ES provides a robust linear regression? This aspect might be critical to assess the practical feasibility of the method, and is worth including in the discussion.

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ED: Publish subject to minor revisions (review by editor) (08 Feb 2021) by Alberto Guadagnini

AR by Gourdol Laurent on behalf of the Authors (26 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (01 Mar 2021) by Alberto Guadagnini

AR by Gourdol Laurent on behalf of the Authors (01 Mar 2021)

Short summary

Electrical resistivity tomography (ERT) is a remarkable tool for characterizing the regolith, but its use over large areas remains cumbersome due to the requirement of small electrode spacing (ES). In this study we document the issues of using oversized ESs and propose a new approach to overcome this limitation. We demonstrate that our protocol significantly improves the accuracy of ERT profiles using large ES and offers a cost-effective means for carrying out large-scale surveys.